1. Field of the Invention
The present invention generally concerns wet shaving systems, more specifically, hand-held razors having both concave and convex cutting surfaces in order to optimize shaving of various body contours.
2. Background Of The Invention
Typically, safety razors have one or more blades, each having one or more sharp edges, supported in a flat razor head assembly between a lower guard bar and seat combination and cap member. The guard bar and cap members cover virtually the entire surface of the blade with the exception of the cutting edges which are left exposed, slightly behind the guard bar. The guard bar is configured and angled, and the blade is positioned in relation thereto, so as to provide a preferred angle between the blade and surface to be shaved when the assembly is drawn over the shaving surface.
Razors of this type work satisfactorily on planar shaving surfaces. The human body, however, has few if any planar surfaces, thus, razor blades are virtually always drawn over a curved surface, particularly in the chin and neck areas of men and the legs and underarms of women. In these areas, a planar blade is an inefficient cutting instrument requiring repeated strokes in order to effectively remove hair. In such conventional razors, the razor head cannot properly conform to curved shaving surfaces because the cap and guard members are made of relatively stiff metal or plastic, particularly when arranged in a sandwich configuration with the blade.
Numerous patents have recognized the desirability of having curved blades which conform to curved shaving surfaces. For example, see Zumwalt, U.S. Pat. No. 1,821,825 which discloses a razor that has a flexible blade that can be installed in either a convex or concave position. Similarly, Ohmer, U.S. Pat. No. 2,008,591, discloses a razor having a flexible blade that may be held in either a convex or concave position. In both patents, the razor must be disassembled to switch from convex to concave cutting surfaces.
Van Cleve, U.S. Pat. No. 4,208,791, discloses a razor cartridge that is shaped to conform to both concave and convex body portions. On one side is a cutting surface in a concave position, while the other side has a cutting edge shaped in a convex position. The user rotates the handle to go from the concave to the convex position. However, the razor is designed for shaving only the legs and underarms and consequently the blades are not at the angle which shavers have become accustomed to in shaving the face and neck.
Recent efforts have been directed toward enhancing the spanwise flexibility of razors for curved surface shaving using various razor head configurations. U.S. Pat. No. 4,854,043, issued to Chen, proposes a flexible razor head, claiming a blade cartridge stiffness wherein 45-90 grams of load produces a spanwise deflection of 0.50 inches. Any such flexible razor requires significant forces delivered by the user in order to achieve cartridge conformity to curved body surfaces. Additionally, as the extent of body curvature increases, the amount of force required to flex the cartridge must also increase in order to conform it to the curvature of the body surface being shaved. Use of such forces to achieve adequate blade curvature often results in cuts or nicks in the surface being shaved.
Some other patents that disclose razors having flexible blades that can be moved into curved cutting positions, include those of Stover, U.S. Pat. No. 2,582,176, and Radcliffe, U.S. Pat. Nos. 4,942,662 and 4,993,154. U.S. Pat. No. 4,459,744, issued to Esnard, discloses a razor that flexes between concave and convex shapes in correspondence with the surface to be shaved and by the force applied thereto. Such razors typically are not able to maintain precise cutting edge geometry due to the flexing of the blade and cartridge.
There are several disadvantages associated with flexible shaving razors. First, the user must become familiar with new shaving techniques and apply additional forces in order to obtain flexure of the cartridge. Any additional force against the skin beyond that required when using a conventional flat razor, can result in skin irritation and accidental shaving nicks.
Second, precise blade cutting edge geometry (the angle and distance relationship between the blade cutting edge and the leading guard or so called soap bar), is very important in achieving a close, comfortable shave. This precise geometry is very difficult to maintain through the parameters of flexure of flexible shaving cartridges, and can result in additional accidental shaving nicks.
Having examined the disadvantages of both conventional flat blade cartridges and flexible safety razors, it is not surprising that the prior art is laden with various proposals which address the body curvature problem from a different approach. Many designers have recognized the need for a safety razor with a built-in curved cutting edge which reasonably matches body curvature. However, none of the references cited disclose a cartridge having a fixed concave blade on one side and a fixed convex blade on the other, which is selectively rotatable into either position.